Magnetic Bearing: Types, How It Works, and Key Applications

When power is lost to an active magnetic bearing, the rotor drops onto the auxiliary (touchdown) bearings. These are rolling-element bearings with a small clearance relative to the magnetic bearing gap. They are designed to safely support the rotor at full speed and allow it to spin down without contact with the electromagnet poles. The drop event is controlled and the machine comes to rest on the touchdown bearings. Every AMB system is required to include touchdown bearings, and every installation should include an uninterruptible power supply (UPS) to provide power for an orderly controlled rundown sequence rather than an immediate drop, which minimizes wear on the touchdown bearings.

In general, no. Magnetic bearings have a lower load capacity per unit of bearing diameter than rolling-element or fluid-film bearings. A rolling-element bearing of 100 mm bore might support a static load of several hundred kN; a magnetic bearing of similar outer diameter supports perhaps 10–30 kN depending on the electromagnet design and allowable power dissipation. This is why magnetic bearings are rarely used in applications requiring high radial loads at moderate speeds — their advantage is in high speed, precision, contamination sensitivity, or maintenance-free operation, not raw load capacity. Rotors for magnetic bearing systems must be designed with this load limitation in mind from the outset.

The magnetic bearing stator and rotor components — the laminations, coils, and housings — are not wear parts and do not have a defined fatigue life in normal operation, because there is no contact between them. The limiting wear components are the touchdown bearings, which are replaced on a preventive schedule, typically every 3–5 years or after a specified number of rotor drop events. The electronics (power amplifiers, controller boards) have expected service lives of 10–15 years, with component-level repair or board replacement as needed. Field reports from pipeline and process compressor installations indicate that magnetic bearing machinery has operated for over 20 years with the original bearing hardware in service, with only touchdown bearing and electronics maintenance.

Yes, magnetic bearing systems can be and are used in ATEX/IECEx classified hazardous areas. The electromagnets and sensors inside the bearing housing are in contact with the process gas, and these components can be designed and assessed for use in flammable gas environments. The control cabinet and power amplifiers are typically located outside the hazardous area in a safe room, connected to the bearing by screened cables. This separation of the active electronics from the hazardous area is standard practice in natural gas compression installations. Users should verify that the specific product configuration has the appropriate hazardous area assessment for their zone and gas group.

Both use controlled magnetic forces to levitate an object without contact, but the applications and scales are different. Maglev transportation systems levitate and propel an entire train vehicle along a guideway, requiring large-scale linear electromagnetic infrastructure. Magnetic bearings support rotating shafts in machines — compressors, turbines, spindles, flywheels — and are a component within a larger machine rather than a transportation system in their own right. The underlying physics and control principles are closely related; in fact, active magnetic bearing research contributed directly to the control methods used in modern commercial maglev rail systems such as the Shanghai Transrapid line and the Japanese SCMaglev. At the functional level, a magnetic bearing is essentially a maglev system applied to a rotating axis within a machine housing.

Retrofit is technically possible but requires significant engineering work. The rotor must be modified or replaced to add the bearing landing journals with appropriate material and geometry, and the bearing housing must be redesigned to accommodate the electromagnet stators, sensors, and auxiliary bearings. The rotor dynamics will change with the new bearing stiffness and damping characteristics, so a full rotordynamic analysis and re-assessment of critical speeds is required. In some cases, the existing rotor design is compatible with magnetic bearing retrofitting; in others, a new rotor is needed. Several companies — including Waukesha Bearings and SKF Magnetic Mechatronics — have performed retrofit projects on centrifugal compressors, and published case studies are available from the Turbomachinery and Pump Symposia proceedings (Texas A&M University).

Temperature affects several components of a magnetic bearing system in different ways. The remanent flux density of permanent magnets decreases with increasing temperature — this is a primary design constraint for hybrid bearings using rare-earth permanent magnets, which can lose significant force capacity at temperatures above 150°C. The winding insulation in the electromagnet coils sets an upper temperature limit for the bearing stator; high-temperature class H or class N insulation extends this to 180°C or 200°C respectively. The ferromagnetic lamination material loses permeability as it approaches its Curie temperature (around 770°C for iron), reducing bearing force at very high temperatures. At the low end, cryogenic operation at liquid nitrogen or liquid helium temperatures is feasible — turbo-expanders in air separation plants and LNG facilities operate with magnetic bearings at cryogenic process gas temperatures.

By installed base volume, the oil and gas / natural gas compression sector is the largest industrial user of active magnetic bearings in large turbomachinery. Vacuum equipment for semiconductor manufacturing is the largest user by unit count. Building HVAC is a growing segment driven by the adoption of magnetic bearing chillers by major brands. Medical device — specifically implantable cardiac assist devices — is a small but high-value market where the technology has become the clinical standard of care for advanced heart failure support. Energy storage via flywheels is an emerging segment with growing installations in grid frequency regulation.